1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display (LCD) device and method for fabricating the same that can reduce the fabrication time and costs by using a lift-strip process.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices are widely used for flat panel displays because of their high contrast ratio, great gray scale and image display, and low power consumption.
An LCD device includes various patterns on a substrate such as gate and data lines that are formed by a photolithography process. For example, a photoresist, which is sensitive to ultraviolet rays, is coated on a substrate and a photoresist pattern is formed by exposure and development processes using an optical mask. Then, various layers are etched using the photoresist pattern as a mask, and the photoresist pattern is stripped. Accordingly, research has actively been conducted to reduce the number of photolithography processes and improve productivity.
An LCD device generally includes a TFT array substrate, a color filter substrate, a liquid crystal layer and a driving circuit. The TFT array substrate includes a gate line layer, a gate insulating layer, a semiconductor layer, a data line layer, a passivation layer and a pixel electrode. In general, five to seven masks are required to form the TFT array substrate. As the number of masks increases, the number of photolithography steps and the probability of process errors also increase.
FIGS. 1A to 1E are cross-sectional views illustrating a method for fabricating a TFT array substrate of an LCD device according to the related art.
Referring to FIG. 1A, a low-resistance metal material, for example, copper (Cu), cupper alloy (Cu Alloy), aluminum (Al), aluminum Neodymium (AlNd), molybdenum (Mo), or chrome (Cr), is deposited on a substrate 11, and then a photolithography process using a first mask is applied to the substrate 11 to form a plurality of gate lines (not shown), a gate electrode 12a and a gate pad electrode 22.
The aforementioned photolithography process is performed in the following steps. First, a low-resistance metal material is deposited on a glass substrate, and then a photoresist is coated on the deposited metal material. After a first mask having a pattern layer is aligned with the photoresist, light is exposed to the photoresist and a developer is applied to the photoresist exposed to the light to form a photoresist pattern. Next, the metal material exposed by the photoresist pattern is selectively etched to form a desired pattern of the deposited metal material on the glass substrate.
Referring to FIG. 1B, an inorganic insulating material including silicon nitride SiNx or silicon oxide SiOx is deposited on an entire surface of the substrate including the gate electrode 12a at a high temperature to form a gate insulating layer 13. Then, an amorphous silicon layer is deposited on the gate insulating layer 13 and is then patterned by a photolithography process using a second mask to form an island-shaped semiconductor layer 14 on the gate insulating layer 13. The semiconductor layer 14 overlaps the gate electrode 12a. 
Referring to FIG. 1C, a low-resistance metal material including copper (Cu), aluminum (Al), aluminum Neodymium (AlNd), molybdenum (Mo), or chrome (Cr) is deposited on an entire surface of the substrate including the semiconductor layer 14 and is then patterned by a photolithography process using a third mask to thereby form a data line layer. The data line layer includes a data line (not shown) formed substantially perpendicular to the gate line to define a unit pixel region, source and drain electrodes 15a and 15b overlapping both sides of the semiconductor layer 14 and a data pad electrode 25 at a pad area.
As disclosed above, the deposited gate electrode 12a, the gate insulating layer 13, the semiconductor layer 14 and the source and drain electrodes 15a and 15b form a thin film transistor (TFT) for controlling the on/off states of the unit pixel region.
Referring to FIG. 1D, an organic insulating material including BCB or an inorganic insulating material including SiNx is formed on an entire surface of the substrate including the drain electrode 15b to thereby form a passivation layer 16. The passivation layer 16 is selectively removed to form a contact hole 71 exposing the drain electrode 15b, a first pad open region 81a exposing the gate pad electrode 22 and a second pad open region 81b exposing the data pad electrode 25 by a photolithography process using a fourth mask.
Referring to FIG. 1E, a transparent conductive material including ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) is deposited on an entire surface of the substrate including the passivation layer 16, and then a pixel electrode 17 electrically connected to the drain electrode 15b and a transparent conductive layer 27 covering the first and second pad open regions are formed in the active area and the pad area, respectively, by a photolithography process using a fifth mask, thereby completing the fabrication of the TFT array substrate. The transparent conductive layer 27 covering the first and second pad open regions prevents the gate and data pad electrodes from being oxidized.
The method for fabricating an LCD device according to the related art is, however, disadvantageous in that it requires five photolithography processes to form the gate line layer, the semiconductor layer, the data line layer, the contact hole of the passivation layer and the pixel electrode. As the number of photolithography processes increases, the fabrication process becomes complicated and the fabrication time and costs increase.